The present invention relates to forming receptacles and methods for receiving particulate material thereon, and thereby fabricating particulate congregates for use as absorbent cores in personal care absorbent articles. More particularly, one of the contemplated applications for the present invention is in a forming drum comprising a plurality of forming receptacles designed and configured to form particulate congregates for use as absorbent cores in personal care absorbent articles.
Current forming media used to form particulate congregates for use as absorbent cores in personal care absorbent articles comprises a perforated plate or woven screen having a 20xc3x9720 or 30xc3x9730 thread weave per inch wherein the holes are arranged in a rectangular pattern. While the geometry of the known art is functional, such geometry does have significant drawbacks.
The holes arranged in a rectangular pattern, typical of woven screens and perforated plates used in the art, does not facilitate optimum formation of personal care absorbent articles because the fraction of the open area represented by the holes in the screen or plate, is so low as to impede desired rates of air flow through the screen or plate. There is a need for a more porous media.
The inventors herein have discovered that rectangular arrangement of the forming media holes is less efficient than improved media of the invention.
The hole size of the conventional screens is nearly twice the size of an average particle of super-absorbent material (SAM) as may typically be used in fabricating personal care absorbent articles. SAM lost by passing through the e.g. screen or perforated plate results in significant in-process loss that must be compensated for by overfeeding the SAM system.
The conventional hole arrangement is also subject to plugging, caused by a single particle, or multiple particles, of SAM getting lodged into a single perforation or hole. Compressed air is periodically used to dislodge as many of the plugged holes as possible. Over the course of a few weeks, screens become significantly plugged, the machine must be shut down, and the screens must be removed and steam cleaned, thus significantly hindering the quality and rate of operation for production of significant elements of personal care absorbent articles.
Screen plugging is also a common occurrence with woven wire screens. The weaving of the wires creates xe2x80x9cpinch pointsxe2x80x9d that trap fibers. The pinch points also become more severe as a flat screen is distorted into the three-dimensional shape of a pocketed forming surface. The pinch points tend to become an even greater problem as the what-was square or rectangular shaped openings of the screen become distorted into a rhombus or diamond-shape through the process of forming a receptacle. This distortion, or pinching off, of the holes can create a significant amount of pinch points and can be severe enough that localized areas of the screen have significantly poor porosity. Thus, different areas of the screen have different porosities, resulting in different air flow rates through the screen at the different areas. Different air flow rates define respective different levels of accumulation of absorbent core material, e.g. fiber and SAM, at the respective different areas, whereby the interval uniformity, or thickness, within a given absorbent core so produced may be less than desired.
The problem for the present invention is thus to provide forming media, as well as methods, for receiving particulate material thereon, and thereby fabricating particulate congregates for use as absorbent cores in personal care absorbent articles, whereby the holes in the forming media are not arranged in a rectangular array, and whereby the configurations of individual ones of the holes in the forming media discourage plugging of the forming media.
It is an object of this invention to create a geometric mismatch between SAM particles and respective forming media holes, by employing hole configurations which reduce the frequency of SAM particles getting lodged in the holes and thus reducing or closing off air flow through the respective holes.
It is another object of this invention to create forming media, void of pinch points and burrs which catch SAM particles and promote plugging, by employing forming media which are manufactured to be absent such pinch points and burrs.
It is yet another object of this invention to improve on the current linear arrangement of holes in forming media, by employing a hole arrangement which promotes improved airflow.
It is still another object of this invention to improve effectiveness of airflow throughout the forming area, by employing forming media having optimum porosity.
In a first family of embodiments, the invention comprises a forming receptacle. The forming receptacle is adapted and configured to receive particulate material thereon, including super-absorbent particles, for thereby fabricating particulate congregates for use as absorbent cores in personal care absorbent articles. The forming receptacle comprises sheet material defining a bottom wall of the receptacle, and a side wall of the receptacle extending upwardly from the bottom wall thereby to define a particulate-receiving cavity in the receptacle. The bottom wall and the side wall have, in combination, a first major surface disposed toward the cavity, an opposing second major surface disposed away from the cavity, and a thickness between the first and second major surfaces. The forming receptacle also comprises an array of apertures extending through the bottom wall, and optionally through the side wall, and connecting the first and second major surfaces, and further comprises a matrix of the sheet material between respective ones of the apertures and defining outer perimeters of respective ones of the apertures.
In some embodiments, the bottom wall and the side wall, in conjunction, comprise a particulate receiving cavity having a depth of at least about 0.001 inch to about 2.00 inches. Yet in other embodiments, bottom wall and the side wall, in conjunction, comprise a particulate receiving cavity having a depth of about 0.00 inch.
In some embodiments, the apertures comprise aperture walls extending from the first major surface to the second major surface, the respective aperture walls tapering generally outwardly from central axes of the respective apertures, and from the first major surface toward the second major surface.
In some embodiments, the aperture walls define cross-sectional areas of such apertures along the thickness of the sheet material, including a first locus defining a smallest cross-sectional area, and a second locus defining a relatively larger cross-sectional area displaced from the smallest cross-sectional area and disposed, from the first locus, toward the second major surface of the sheet material. The smallest cross-sectional area can be displaced from and between both of the first and second surfaces.
In preferred embodiments, the apertures can define cross-sectional areas proximate the first and second surfaces, the cross-sectional area proximate the second surface being greater than the cross-sectional area proximate the first surface.
In some embodiments, the apertures comprise aperture walls extending generally perpendicular to the first surface from loci adjacent the first surface to interior loci between the first surface and the second surface, and tapering generally outwardly from the interior loci to the second major surface, whereby open areas defined by the respective apertures at the second major surface are greater than open areas defined by respective ones of such apertures at the first major surface.
In some embodiments, the aperture walls taper inwardly from the first major surface and toward the second major surface, to a throat zone, and taper outwardly from the throat zone to the second major surface, such that the throat zone defines an opening smaller in cross-section than corresponding openings defined by the respective aperture at either of the first or second major surfaces.
In some embodiments, a respective aperture defines an opening at the first major surface, the opening having an open area corresponding to the area of a circle having a diameter of at least about 0.009 inch, up to about 0.040 inch, preferably at least about 0.010 inch, up to about 0.025 inch, more preferably at least about 0.011 inch, up to about 0.015 inch.
In some embodiments, the matrix of sheet material at the first major surface generally has a minimum projected width between respective ones of the apertures of about 0.003 inch to about 0.015 inch, preferably about 0.005 inch to about 0.009 inch.
In preferred embodiments, aperture walls of adjacent ones of the apertures intersect the second major surface without intersecting each other, wherein such aperture walls of adjacent first and second ones of the apertures define nominal distances therebetween without intersecting each other.
In preferred embodiments, the matrix of sheet material at the second major surface generally has a minimum width between respective ones of the apertures of about 0.0007 inch up to about 0.004 inch, preferably about 0.0007 inch up to about 0.003 inch, more preferably about 0.001 inch up to about 0.002 inch.
In preferred embodiments, the array of apertures is arranged in a series of parallel rows of apertures, wherein spacing between apertures in a given row is substantially constant from row to row, and wherein the rows are displaced laterally with respect to each other such that adjacent apertures in adjacent rows define angles of about 50 degrees to about 90 degrees, in some more preferable embodiments about 50 degrees to about 70 degrees, yet in other more preferable embodiments, about 80 degrees to about 90 degrees, with respect to an imaginary line parallel to the rows. Yet in some embodiments. the array of apertures is arranged sporadically, wherein spacing and orientation between apertures in a given row is substantially variable.
In highly preferred embodiments, the apertures, measured at a smallest cross-section of opening defined by each such aperture, in combination, define a composite open area representing at least about 35 percent, preferably greater than 40 percent, of the combined areas of the bottom wall and the side wall.
Thickness of the sheet material is preferably about 0.003 inch to about 0.030 inch, and more preferably about 0.005 inch to about 0.015 inch. Length of the receptacle is preferably about 10 inches to about 30 inches, more preferably about 12 inches to about 24 inches. Structures of the apertures can reflect photochemical machining.
Some embodiments comprise forming drums designed and configured to form, in a continuous process, particulate congregates for use as absorbent cores in personal care absorbent articles. Such forming drums can comprise mounting structure for mounting the forming drum about an axis of rotation, and forming receptacle repositories extending about at least a portion of a circumference of the forming drum and supported from the mounting structure. The forming receptacle repositories include ones of forming receptacles mounted about the circumference of the drum. The forming receptacles are effective to receive and accumulate thereon elongate fibers, and particles of super-absorbent material, thereby to form such congregates. Yet other embodiments comprise forming drums which can comprise mounting structure for mounting the forming drum about an axis of rotation, and a forming receptacle, the forming receptacle being uniform and continuous, and extending about substantially an entire circumference of the forming drum and supported from the mounting structure.
In a second family of embodiments, the forming receptacle comprises a substrate defining a bottom wall of the receptacle, and a side wall of the receptacle extending upwardly from the bottom wall thereby to define a particulate-receiving cavity in the receptacle. The bottom wall and the side wall, in combination, comprise elements defining a first major side disposed toward the cavity, an opposing second major side disposed away from the cavity, and a thickness between the first and second major sides. An array of apertures extends through the bottom wall, and connects the first and second major sides. Aperture walls define cross-sectional areas of such apertures along the thickness of the substrate, including a locus defining a smallest cross-sectional area, and a locus defining a relatively larger cross-sectional area displaced from the smallest cross-sectional area and disposed toward the second major side of the substrate.
In some embodiments, the forming receptacle further comprises a matrix of the substrate between respective ones of the apertures, and defining outer perimeters of respective ones of the apertures, wherein the aperture walls extend from the first major side to the second major side, and wherein respective said aperture walls taper generally outwardly between the first major side and the second major side.
In preferred embodiments, the apertures, measured at a smallest cross-section of opening defined by each such aperture, in combination, define a composite open area representing at least about 35 percent, preferably, greater than 40 percent, of the combined areas of the bottom wall and the side wall.
In a third family of embodiments, the invention comprehends a method for forming a congregate of particulate material for use as an absorbent core in an absorbent article, wherein the particulate material comprises generally particles, optionally spherically-shaped particles, of super-absorbent material. The method comprises conveying the particulate material in a gaseous carrier toward a forming receptacle. The forming receptacle comprises sheet material defining a bottom wall of the receptacle. The sheet material also defines a side wall of the receptacle extending upwardly from the bottom wall. The bottom wall and the side wall, in combination, define a particulate-receiving cavity in the receptacle. The bottom wall and the side wall have, in combination, a first major surface disposed toward the cavity, an opposing second major surface disposed away from the cavity, and a thickness between the first and second major surfaces. An array of apertures extend through the bottom wall and define passage ways between the first and second major surfaces. The passage ways are defined by aperture walls which taper generally outwardly from central axes of the respective passage ways, and from proximate the first major surface toward the second major surface. The passage ways tend to generally progressively expand in cross-sectional area as one progresses toward the second major surface, and projected areas of the particles of the super-absorbent material are generally larger than projected areas of the apertures. The method further comprises receiving and collecting particles of the particulate material in the cavity and thereby forming the congregate while generally not conveying particles of the super-absorbent material into the passage ways. Undersize particles of super-absorbent material which do enter respective ones of the passage ways tend to pass entirely through the passage ways and not become lodged in such passage ways because of being released to pass through such passage ways, by the generally progressively expanding cross-sections of such passage ways along the direction of travel of such particles.
In some embodiments, the projected area of a respective such aperture is defined by a relatively more constrictive throat zone of the respective passage way, the throat zone being disposed closer to the first major surface than to the second major surface.
A projection of such throat zone is typically no more than 25 percent, preferably no more than 15 percent, smaller in cross-sectional area than a projection of the respective aperture at the first surface. In some embodiments, a projection of the throat zone is substantially the same size in cross-sectional area as a projection of the respective aperture at the first surface.
In preferred embodiments, the method comprises receiving and collecting the particles of a such forming receptacle wherein the particles of super-absorbent material are generally oblong-shaped, having a length-to-width ratio of no more than 4/1.